1. Field of the Invention
The invention relates to an automatically-closing screen door, typically for enclosure with a conventional sliding glass door used for patio entry in residential and/or commercial dwellings. More particularly, the invention relates to an automatically-closing screen door in which a counterweight is employed to provide a controllable closing force to the door.
2. Description of the Related Art
Sliding glass door assemblies have become commonplace in both residential and commercial dwellings. A sliding door is mounted on a horizontal track in offset alignment with a fixed door. When an occupant of a dwelling desires to enter or leave the dwelling, the occupant slides the sliding door along the track to open and close the sliding door with respect to the fixed door.
In addition to having a sliding glass door, many sliding glass door assemblies have a sliding screen door as well mounted for sliding movement on a track that is generally parallel to the horizontal track for the sliding glass door. The sliding screen door allows the sliding glass door to be left in an opened position to allow airflow into the dwelling while preventing insects and other undesirable entities from entering the dwelling.
Sliding screen doors are typically moved between opened and closed positions by an occupant grasping a handle on the screen door and manually sliding the sliding screen door between the opened and closed positions. This is acceptable if the sliding screen door is maintained in the closed position.
However, if the sliding screen door is left in an open position, the sliding screen door does not return to the closed position on its own accord. This can be a problem if the occupant has young children who frequently forget to close the sliding screen door after entering or leaving the dwelling. In addition, if the occupant is entering or leaving the dwelling carrying an object or performing an activity that requires both of the occupant's hands (e.g., carrying trays of food), it may also be difficult to manually close the sliding screen door in an acceptable amount of time.
One solution to these problems has been to add a spring (e.g., a coil spring or a bungee cord) which is attached at one end to the sliding screen door and at an opposite end to a frame surrounding the sliding screen door. The spring thereby biases the sliding screen door to the closed position.
These spring-based automatic closure systems have some problems. First, the resistance on the screen door increases as you open the door since the return force of a spring-based system is proportional to the length it is extended (see Hooke's law where the spring force F=kx). Second, when a spring-based automatic closure system is released so that it travels from the opened position to the closed position, it can close very quickly as a result of the conversion of the potential energy stored in the extended spring into the kinetic energy as the sliding screen door moves toward the closed position. Third, repair of these so-called spring-based automatic closure systems can be difficult and costly. Fourth, the spring used in the so-called spring-based automatic closure system can lose elasticity over time and require replacement.